Portable information terminals such as mobile phones and PDAs (Personal Data Assistant) use LED (Light-Emitting Diode) elements for various purposes. For example, LED elements are used as backlight for an LCD (Liquid Crystal Display) and flash for a camera employing a CCD (Charge-Coupled Device). In addition, LED elements having different emission colors are blinked as illumination.
A method for adjusting a luminance of an LED by PWM (Pulse Width Modulation) control has been known. This is a method to adjust the luminance of the LED by changing a pulse width (duration) of a current flowing through the LED, i.e., by changing a duty cycle of the pulse of the current flowing through the LED.
For example, Japanese Patent Laying-Open No. 7-321623 (Patent Document 1) discloses a drive circuit (MOS (metal oxide semiconductor) drive circuit) as described below. More specifically, a MOS drive circuit for driving a light emitting or a display array having a plurality of current-driven elements connected in parallel includes a MOS array having a plurality of MOS elements connected in parallel and supplying a driving current to each current driven element, a switching circuit separately and independently provided for each MOS element, a voltage source for supplying a control voltage to each MOS element via each switching circuit, and an operational amplifier provided between the voltage source and the switching circuit.
Patent Document 1: Japanese Patent Laying-Open No. 7-321623